1. Field of the Invention
The invention relates to a polyaxial bone anchoring device that includes a bone anchoring element for anchoring in a bone, a head receiving part for receiving a head of the bone anchoring element, a locking ring mounted around the head receiving part for coupling a stabilization rod to the head receiving part and the bone anchoring element, a cap for securing the rod, and a locking element for locking the assembly. Upon connection of the cap to the head receiving part, a sub-assembly of the locking ring, the rod, and the cap is rotatable with respect to the head receiving part. The locking element exerts pressure onto the rod to move the locking ring to a position that locks the head in the head receiving part and fixes the rod simultaneously. The polyaxial bone anchoring device is particularly suitable for providing an enlarged pivot angle for the bone anchoring element relative to the rest of the device.
2. Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle is described in U.S. Pat. No. 6,736,820. This bone anchoring device includes a bone screw and a receiving part with a seat for the head of the bone screw. The screw member can be pivoted to at least one side by an enlarged angle, because the edge of the free end of the receiving part is of asymmetric construction.
Another polyaxial bone anchor is described in US 2005/0080415 A1. This bone anchor has a body member having a U-shaped channel for receiving the rod and a compressible recess for receiving a head of the anchor member such that the anchor member can initially polyaxially angulate with respect to the body member and further has a collar slideably disposed about the body member and capable of compressing the recess around the head. The lower bounding edge of the body member may include a counter-sunk region to permit increased angulation, when the anchor member is oriented toward the counter-sunk region.
US 2009/0149887 A1 describes an apparatus for connecting a bone anchor to a support rod that includes a connector body and a cap.